Sweet syrups consisting of sucrose (cane sugar) or dextrose-containing products obtained from starch hydrolysis are widely used in the baking, confectionery and beverage industries. Syrups containing a mixture of glucose and fructose are also widely used in industry because of their sweet taste (sweeter than sucrose) and low tendency to crystallize. Such syrups are commonly produced from glucose syrups using a glucose isomerase to catalyze the isomerization of glucose to fructose. While glucose is somewhat less sweet than sucrose, fructose is considerably sweeter than sucrose so that the overall sweetness of the treated glucose syrup is greater than that of sucrose. Glucose isomerases can be obtained from a large number of species of microorganisms.
In a typical method for the production of glucose isomerase, the microorganisms are cultivated on media containing inorganic salts and sources of carbon and nitrogen at a pH between pH 5 and pH 9. Microorganisms suitable for use in this method have been extensively characterized as is described by Buck, in Enzyme and Fermentation Biotechnology, Halsted Press, London, Pp 147-171 (1977). The use of many of the microorganisms useful for the production of glucose isomerase requires the introduction of xylose or a xylose-containing compound to the growth medium in order to induce glucose isomerase formation. However, pure xylose is too expensive to be used in commercial fermentation processes thereby rendering desirable mutant strains which, when cultivated, are capable of metabolizing carbon sources other than xylose. The random screening of mutant strains of cells from the Bacillus genus is extremely burdensome since it is often necessary to screen thousands of mutants in order to obtain one having the desired properties.
Novo Industri A/S has disclosed the production of .alpha.-amylase from Bacillus licheniformis in Process Biochem., 10 (4), 17-19 (1975) and copending application Ser. No. 156,496, filed June 4, 1980 and commonly assigned herewith discloses the use of Bacillus licheniformis in the production of glucose isomerase.